1. Field of the Invention
This patent specification relates to packaging for downhole pressure transducers and, more particularly, to techniques for providing volume changes and/or reduced thermally induced pressure changes in sealed containers for downhole pressure transducers.
2. Background of the Invention
In measuring pressure in a downhole environment, a variety of pressure transducer technologies can be used. For example, helical bourdon tube gauges, strain gauges, quartz crystal gauges, and MEMs based sensors have been proposed and/or used downhole. For downhole applications, the pressure transducer is typically sealed in a package so as to isolate the transducer from the harsh downhole environment. For example, the packaging serves to protect the transducer from caustic and potentially fouling oil and/or drilling mud found in the downhole environment. Within the sealed package a substance such as silicone oil can be used to transmit the pressure to the transducer. Silicone oil is often used due to its relatively low compressibility, high boiling point and inertness. In order for the sealed packaging to be effective, the package must not only isolate the inner and outer environments. The package should also adequately transmit the pressure from the outside of the package to the inside by changing its volume in response to the external pressure change. Furthermore, the package for downhole use also needs to be able to change its volume to accommodate relatively large changes in temperature between the surface and various downhole environments.
In conventional designs, a bellows system is typically used to provide the needed isolation and pressure transmission capabilities. A bellow system is characterized in that the primary direction motion is primarily perpendicular to the surface of the bellows. However, bellows systems tend to be rather large relative the sensor package, and are prone to problems such as mud clogging. Mud may get into the bellows grooves and harden, thereafter preventing the bellows from operating properly. Bellow systems are also relatively difficult to clean thereby making it more difficult to avoid problems such as mud clogging. Finally, bellow systems are prone to damage and/or malfunction due to shock when operating in a rugged downhole environment. This is especially true when the bellows aspect ratio is long. Thus, it is desirable to provide a downhole pressure transducer package that alleviates some or all of the drawbacks with conventional bellows arrangements.
As will become apparent from the following description and discussion, the present invention overcomes at least some of these deficiencies and provides an improved pressure transducer housing.